A variety of provers for accurately calibrating a flowmeter are known. For the best accuracy, it is essential that flow measurement devices be proven under actual operating conditions. This is typically done by installing a piston or ball prover in line with the flow measuring device which is to be proven. There are at least two types of meters, however, which do not lend themselves to this type of a proving system. One type of meter is a meter with a slow response time, for example a coriolis mass flowmeter. A coriolis meter requires a set amount of time for acquiring and filtering data updates or flow rate changes. The update is added to the previous information for the current output indicating the flow rate. Five tenths to five seconds may be required for a change in flow rate to be fully registered at the meter's output. As a result, a coriolis meter can only be accurately proven when the flow rate changes are allowed to average each other out. The large fluid volume required to obtain an accurate average signal makes conventional proving equipment unusable. A prover large enough to obtain a valid measurement would be unacceptably large. Other meters have an inconsistent response time. This is a characteristic, for example, of a vortex shedding meter. A vortex shedding meter has an inconsistent pulse frequency when measured over short periods. This is caused by random turbulence even when the flow rate is consistent. However, when the output pulses are averaged over a longer period of time, the average flow rate and total flow is very accurate. Again, the large fluid volume required to obtain the required certainty, makes conventional prover equipment unusable. One approach has been to use several passes of a small volume prover and average the results, however, data variations between each pass are missed and the small volume perturbs the flow rate. As a result, there is a need for a prover system with a long calibration cycle yet, the accuracy traceability of a small volume prover.
At present turbine and other types of flowmeters accurately calibrated in a lab are used as master or transfer provers with long calibration cycles. A turbine flowmeter can provide a calibration cycle as long as desired. However, the accuracy of the calibration performed in situ using a turbine flowmeter calibrated in the lab is limited due to differences between the lab and the test site in the fluid, its temperature, its flow rate and its flow dynamics. Inaccuracies also arise when the turbine meter is transported.